This invention relates to cross switching of digital signal transmission paths which are established in duplex by switch elements controlled by a control device in two switch matrix devices and selected by a transmit or redundancy switching device under control by the control device depending on a failure in the switch elements. Each of the switch matrix devices may be a space matrix switch. The switch elements may be grouped or integrated into printed circuit modules, which may be called switch units. More particularly, this invention relates to a cross connecting method and to a cross connecting network.
A somewhat different cross connecting network is disclosed in U.S. Pat. No. 5,241,550 issued to Toshihiko Kusano, the present inventor. An improved cross connecting network is revealed in prior patent application filed Feb. 16, 1993, by Toshihiko Kusano, the instant inventor, under Ser. No. 08/018,027, now U.S. Pat. No. 5,365,511. The prior patent application is herein incorporated by reference.
In the manner which will later become clear, such a cross connecting network is controlled by a control device to establish a first plurality of network paths for digital signals. Each of the digital signals includes a blank data field at a period predetermined in connection therewith, namely, specific thereto. Such a period may be common to all digital signals. At any rate, the improved cross connecting network comprises first and second switch matrix devices, a preprocessor, a branching device, and a transmit or redundancy switching device.
Each switch matrix device has a device input side and a device output side and includes a second plurality of matrix device paths, where the second plurality is not less than the first plurality. If equal in number to the first plurality, the matrix device paths of each switch matrix device are for transmitting the digital signals, respectively. In the matrix device paths of each switch matrix device, a plurality of switch elements are interposed in each of foremost through last stages. The stages are successively arranged from the device input side to the device output side. In each switch matrix device the switch elements of the stages are controlled by the control device to cross switch the matrix device paths, or the digital signals, into or through cross connected paths. The cross connected paths of the first and the second switch matrix devices thus serve as duplexed parts of the network paths.
A combination of the preprocessor and the branching device is used as a branching arrangement including a plurality of branching arrangement paths, equal in number to the first plurality. The branching device branches the branching arrangement paths into primary branched paths continuous to the branching arrangement paths and secondary branched paths continuous to the branching arrangement paths. The primary and the secondary branched paths serve as additionally duplexed parts of the network paths. On the device input side, the primary branched paths are connected to the matrix device paths of the first switch matrix devices. The secondary branched paths are connected to the matrix device paths of the second switch matrix device. It is possible, if the matrix device paths of each switch matrix device are greater in number than the first plurality, to use the switch elements of the foremost stage of each switch matrix device in selecting the matrix device paths for connection to the branched paths of a pertinent one of the primary and the secondary ones.
The transmit switching device includes as additional parts of the network paths a plurality of switching device paths, not less in number than the first plurality. It will be presumed in each switch matrix device that the matrix device paths are cross switched at a certain current time instant into the cross connected paths. In the manner which will later be described, the control device selects at the current time instant a plurality of acting paths, equal in number to the first plurality, from the cross connected paths of the first and the second switch matrix devices. On the device output sides of the first and the second switch matrix devices, the acting paths are connected to the switching device paths. Others of the cross connected paths of the first and the second switch matrix devices are left unconnected to the switching device paths as standby paths which comprise corresponding paths in one-to-one correspondence to the acting paths.
In the improved cross connecting network, the control device is enabled so to connect the switching device paths to thee acting paths as follows. Switch failure detector elements are connected to the matrix device paths of the first and the second switch matrix devices nearer to the device output side than the switch elements of all stages, namely, whole switch elements, to detect whether-or not the digital signal is transmitted through each of the whole switch elements with an abnormal state. Furthermore, switch demand data generator units are connected to the failure detector elements, respectively. Processor units are connected to the switch demand data generator units and to the matrix device paths of the first and the second switch matrix devices downstream of the respective failure detector elements. A combination of each switch demand data generator unit and the processor unit therefor serves as a switch request flag superposing element for superposing a switch request flag on a predetermined part of the blank data field of each digital signal when the abnormal state is detected by one of the failure detector elements that is connected to the switch request flag superposing element under consideration as a particular failure detector element.
Presence of the abnormal state indicates either that the digital signal in question is wholly or partly lost or that some spurious data are superposed on the digital signal under consideration. Very presumably, a failure is present in one of the whole switch elements that is connected to the particular failure detector element. In other words, one of the acting paths is a defective path when the switch request flag is superposed on the digital signal transmitted therethrough. That is, the switch element in question is a defective element.
Switch request flag detector elements are therefore connected to the switching device paths, respectively, and to the control device. The switch request flag detector element detects the switch request flag in the digital signal transmitted through the defective path and consequently through one of the switching device paths that is connected to the switch request flag detector element under consideration as a particular device path. This switch request flag detector element informs the control device of detection of the switch request flag and of the defective path. The control device selects as a fresh path of the acting paths for connection to the particular device path one of the corresponding paths that corresponds to the defective path.
In the manner described in the foregoing, it is possible with the improved cross connecting network to substitute for the defective path, path by path rather than switch matrix device by switch matrix device, a faultless one of the corresponding paths as the fresh path. While diligently continuing reduction into practice of such a cross connecting network, the present inventor has confirmed that it is highly desirable to locate the defective element.